Electron-gamma spectroscopic measurements in 131Cs

The decay of 131Ba to levels of 131Cs has been studied using an HPGe detector for gamma-ray and a mini-orange electron spectrometer for conversion electron measurements. Our experiment identifies 76 gamma transitions in this decay, including 15 new gamma rays and 6 new K-conversion electron lines. The results also include M2 multipolarity assignment for the 269 keV transition, E2 assignment to two newly observed transitions, M1+E2M1+E2 for the 406 and 417 keV transitions and M3 for the 533.67 keV transition. A revised 131Cs level scheme is proposed. While confirming the existence of 15 well-established levels, we present strong evidence from our beta decay study for five levels at 496, 764, 775, 1044 and 1258 keV which were earlier observed in reaction studies. Spin–parity assignments to a few other levels are also suggested. The level structure of 131Cs is discussed in the light of the intermediate coupling model.